I am a medical and very new to Arduino and programming.
I want to interface pulse oximeter and heart rate monitor using Arduino.
Please find photo of the sensor below:
If you are new to Arduino, I suggest to choose a sensor that is advertised to work with Arduino, and for which there are tutorials that you can understand and follow.
Also note that none of the sensors mentioned actually measure blood pressure. For that you need an inflatable cuff and monitor the pulse when the cuff is fully inflated and also when the pressure is released.
Medical electronics is not a field that beginners start with. Take time to build up your knowledge first.
Just because the board has RXD and TXD labels does not mean that particular model of pulse oximeter will be using those pins. The board is clearly lacking other components, which makes it likely that same board is used in multiple versions of the device.